(1) Field of the Invention
The present invention relates to compositions and methods for inhibiting the corrosive effects of acids on metal pipes. More particularly, the present invention relates to compositions formed by the condensation of a polyamine with tall oil and its derivatives and/or with particular 21 or 22 carbon unsaturated fatty acid or acid anhydrides. Such compositions have been found to be especially effective at protecting metal pipes during oil well stimulation operations where a 15-30% acid solution is used to increase production in oil wells or in the other operations where ferrous metal surfaces are exposed to strong acidic environments, such as pickling baths and industrial cleaning.
(2) Description of the Prior Art
To increase reservoir productivity by acidizing, a corrosive fluid is pumped down into a limestone or dolomite formation to improve formation permeability. The fluid must etch flow channels and dissolve debris to restore the original drainage patterns. In fracture acidizing, acid is pumped down the hole under a pressure greater than the formation pressure creating new channels by fracture. Matrix acidizing is performed by injecting acid at lower pressure than the formation pressure, enlarging the existing flow channels.
Hydrochloric acid (15-30% concentration) alone or blends with hydrofluoric acid or acetic acid are commonly used for this purpose, and to a lesser extent phosphoric acid. Most of the corrosion inhibitors which are being used to protect the steel pipes through which they are pumped into the formations are blends of amines such as dodecyl amines, alkyl aquinolines, alkyl pyridines and acetylenic ethanols, with propargyl alcohol being the most widely used. Compositions for these applications are disclosed in U.S. Pat. Nos. 3,816,322 to Griffin et al., 3,802,890 to Keeney.
Ferrous metals, when being formed into steel sheets, plates, bars, etc., are subjected to elevated temperatures. Exposure to these temperatures results in the formation of a coating of iron oxide on the metal, commonly called mill scale. Before these formed materials can be subjected to further processing, such as, electroplating, galvanizing, cold rolling, etc., this scale must be removed. In commercial operations, this scale is removed by immersing the sheet, plate or bar in a suitable acid solution, called an acid pickling bath. The acid solution attacks and dissolves the scale. Once the scale is dissolved, the acid is then free for further attack upon the metal. In order to reduce this attack on the metal, corrosion inhibitors are added to the pickling bath solution.
Corrosion inhibitors are required which protect a variety of metals in contact with cleaning solutions based on a variety of acids which are used over a wide temperature range. Acids most commonly used are sulfuric and hydrochloric; acids used for specialty applications include phosphoric, sulfamic, oxalic, tartaric, citric, acetic, and formic.
The combination of rosin amine, ethoxylated rosin amine, ethyloctynol and propargyl alcohol as inhibitors for this application is disclosed in U.S. Pat. No. 3,705,106 to Muzyczko et al. Other effective formulations contain organic sulfur compounds as disclosed in U.S. Pat. Nos. 3,773,675 to Heiss et al., in 3,764,543 to Frenier et al. and in 3,809,655 to Williams.
A search of the prior art failed to uncover any prior art reference which discloses the compositions of the present invention or is especially useful in reducing the corrosive effects on metal piping by acidizing fluids containing inorganic acids.
Thus, in U.S. Pat. No. 4,344,861 to Levy, a method of inhibiting the corrosion of metals in contact with petroleum and petroleum fractions using bis-amides is disclosed. The bis-amides are formed by reacting one or more polyamines with a dimeric acid or with a dicarboxylic acid having from 2-12 carbon atoms. Although no specific dimeric acids are listed, those produced by dimerizing fatty acids of 18 carbon atoms are stated to be of particular interest. The major product, as stated, is a bis-amide although imidazoles might be formed when certain polyamines are used. Unlike the present invention, the corrosion inhibitors of Levy are effective against the naturally occurring corrosives in acidizing fluids and not particularly effective when higher concentrations of acids are added to the acidizing fluid to aid in the producing operation. See Tables I, II and VII to follow, wherein the dimer acid-diethylenetriamine condensate of Levy is shown not to be particularly effective against the corrosive action of acid concentrations of as low as 300 mg/l.
U.S. Pat. No. 3,687,847 to Maddox, Jr. et al. discloses a composition for inhibiting corrosion in oil wells. As with Levy, the composition of Maddox, Jr. et al is particularly effective with naturally occurring corrosives such as, H.sub.2 S, CO.sub.2, O.sub.2, brine, and organic acids which are found in natural gas. The composition is formed by first reacting tall oil with a polyamine to yield an imidazole which is then reacted with a dimeric or trimeric fatty acid. The dimer or trimer is formed from a longer chain fatty acid, such as, linoleic or eleostearic, having 18 carbon atoms and then condensed with a polyamine, e.g., imidazoline.
U.S. Pat. No. 3,134,759 to Kirkpatrick et al., discloses a corrosion inhibiting composition comprising the reaction product of tall oil monocarboxy acids with a polyamine to form an intermediate which, in turn, is reacted with only one of the carboxy groups of organic polycarboxy acid containing at least 32 carbon atoms. The resulting product was found useful for protecting well casings from the corrosive action of weak acids, e.g., CO.sub.2, H.sub.2 S, brines, weak inorganic acids, and organic acids, and not the strong inorganic acids normally added to acidizing fluids.
U.S. Pat. No. 2,920,040 to Jolly, discloses a process for inhibiting corrosion of ferrous metals when subjected to corrosive oil well fluid H.sub.2 S, CO.sub.2, and lower organic acids wherein a polyamine is acylated with a monocarboxylic acid, such as, rosin acids or fatty acids, having 8 to 22 carbon atoms. This acylated intermediate forms a salt with an aromatic carboxylic acid.
U.S. Pat. No. 2,646,399, to Hughes, discloses a method for inhibiting corrosion of metals in which a polyamine is reacted with a dibasic acid having 8 or more carbon atoms to form bis-imidazoline. The composition is stated to be useful in inhibiting corrosion resulting from a crude oil/brine mixture.